Chemistry: Post your doubts here!

[sara kamal]

http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_s03_qp_4.pdf
please explain Q2 part b

 

[ZaqZainab]

can anyone tell me the answer and explain why
Please

 

[BreakingBad]

which ions are present in a solution of ethanol in an excess of concentrated sulphuric acid?
1) CH3CH2O^-1
2) CH3CH2^+OH2
3) HSO4^-1

The ions present in a solution of ethanol and H2SO4 are:
2H+
OH-
HSO4-
and the intermediate:
CH3CH2O+

View attachment 34691
Can anyone explain this question?

First:
2AL + 3/2O2 --> AL2O3
Mole ratio is 2:1 so 0.02 mol of Al will give 0.01 mole of AL2O3.

Then:
Al2O3 + 6HCl --> 2AlCl3 + 3H2O
Mole ratio is 1:6 so 0.01 mol of Al2O3 will react with 0.06 mol of HCl completely.

Vol. = Mol/concentration = 0.06/2 = 0.03 dm^3 = 30 cm^3

can anyone tell me the answer and explain why
Please

i)
Ksp = [Mg2+][OH-]^2 (It's the formula of Ksp)
The unit is therefore (mol/dm^3)3 = mol^3dm^-9

ii)
Concentration of Mg = x
Therefore, concentration of OH- for it to be saturated = 2x (because 2 moles of OH- ions react with 1 mol of Mg2+ ion)

Use the formula aboxe:
(x)(2x)^2 = 2*10^-11
4x^3 = 2*10^11
x = 1.71*10^-4 moldm^-3

iii)
The magnesium is saturated y calcium sol. until it reaches saturation. This means that the saturated part is left out. Therefore, the left out part would be:
x/total *100 = (1.71*10^-4/0.054) * 100 = 0.317 %
The % amount taken = % total - % left out = 100 - 0.317 = 99.7 %

can anyone tell me the answer and explain why
Please

The answer is A.
When using atomization energies, we can write the equation as:
C + 2 (H-H) => 4 (C-H)
Atomization energy of C will be given
Atomization of H2 will be given which can be used to calculate H-H:
1/2 H-H = Atomization energy
According to equation:
Formation of methane = bond energy = product energy - reactant energy
B is not the answer because we can only calculate the enthalpy of reaction using those values.
C is not the answer because there is no formula connecting formation and combustion for this question.
D is not the answer because it doesn't make sense.

 

[ZaqZainab]

The answer is A.
When using atomization energies, we can write the equation as:
C + 2 (H-H) => 4 (C-H)
Atomization energy of C will be given
Atomization of H2 will be given which can be used to calculate H-H:
1/2 H-H = Atomization energy
According to equation:
Formation of methane = bond energy = product energy - reactant energy
B is not the answer because we can only calculate the enthalpy of reaction using those values.
C is not the answer because there is no formula connecting formation and combustion for this question.
D is not the answer because it doesn't make sense.

How doesn't D make sense we can just find the formation of CH4 and divide by 4?
Thanks

 

[ZaqZainab]

Can anyone help me out with this one?
Why can't the answer be B??

 

[ZaqZainab]

in the Ms they take Mass as the volume of acid used why is that?

 

[BreakingBad]

How doesn't D make sense we can just find the formation of CH4 and divide by 4?
Thanks

The definition of enthalpy energy of formation is defined as the energy change that takes place when 1 mole of a substance is formed from elements in it's standard state under standard conditions. It has nothing to do with bond energy. To make it clearer, if you take a look at the data booklet, the bond energy of CH bond is 413 kJ/mol while the enthalpy change of formation of CH4 is -75 kJ/mol.

 

[ZaqZainab]

The definition of enthalpy energy of formation is defined as the energy change that takes place when 1 mole of a substance is formed from elements in it's standard state under standard conditions. It has nothing to do with bond energy. To make it clearer, if you take a look at the data booklet, the bond energy of CH bond is 413 kJ/mol while the enthalpy change of formation of CH4 is -75 kJ/mol.

thanks so much could you help me with 2 other questions please

in the Ms they take Mass as the volume of acid used why is that?

Can anyone help me out with this one?
Why can't the answer be B??

 

[BreakingBad]

Can anyone help me out with this one?
Why can't the answer be B??

The answer cannot be B because if we use the combustion values we need 1 mole of PbO, in which case it will no longer have 1 mole of Pb3O4 and we will not be able to equate the formation and combustion values. The answer is D because when both values of formation are given we can simply use the formula and get our answer.

in the Ms they take Mass as the volume of acid used why is that?

Have they used 20 cm^3?

 

[ZaqZainab]

Have they used 20 cm^3?

they have used 30 cm^3 as the MASS but 30 cm^3 is the volume of the acid used? do we always just take volume instead of mass?

 

[BreakingBad]

they have used 30 cm^3 as the MASS but 30 cm^3 is the volume of the acid used? do we always just take volume instead of mass?

That is actually not so surprising because for liquids or aqueous substances, the formula for energy gained is in fact q=Vc(T2-T1).

 

[ZaqZainab]

That is actually not so surprising because for liquids or aqueous substances, the formula for energy gained is in fact q=Vc(T2-T1).

it was for me i did'nt know that as i just started my AS
thanks for your help

 

[Pwetty Angel]

they have used 30 cm^3 as the MASS but 30 cm^3 is the volume of the acid used? do we always just take volume instead of mass?

remember mr manoj's notes??? he said 1gm= 1cm^3 ... so 30cm^3 would be 30gms.
am soorry am late.

 

[SomeStudent]

I dont get moles.. of both AS and A2. My book has only got two pages of it.

 

[SomeStudent]

I dont get moles.. of both AS and A2. My book has only got two pages of it.

 

[goodluckayesha]

http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_s09_ms_5.pdf
http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_s09_qp_5.pdf
can anyone kindly explain Q1 part c,d,e,f and post the diagram for c
thnx in advance

 

[Dykhoo]

Anyone has Cambridge International AS and A Level Chemistry Coursebook ebook 2011 edition ? I need the ebook urgently . Please email to me at [email protected]

 

[Abdel Moniem]

http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_w05_qp_1.pdf Question 12

 

[xhallay]

AoA, please answer this for me.. A 5g sample of an anhydrous group 2 metal nitrate loss 3.29g mass on strong heating. What metal is present. How do u solve it?

 

[MiniSacBall]

AoA, please answer this for me.. A 5g sample of an anhydrous group 2 metal nitrate loss 3.29g mass on strong heating. What metal is present. How do u solve it?

Would you like to mention the full question please, there must be more added to this question. You just can't tell it simply that it is this element or this. Well All the nitrates in Group 2 undergo thermal decomposition to give the metal oxide, nitrogen dioxide and oxygen. So i just can't simply say that it is Mg, Ca ...etc. Also as you go down the group, these metal nitrates become more stable to heat. So you need to heat Ca more than Mg. Because Ca is below Mg, thus it is more heat stable than Mg.

Hope this helps ,
I am As student so i have told you what i have learnt, and that it supported the question.